1. Field of the Invention
The present invention relates to novel amorphous alloys resistant against hot corrosion in sulfidizing and oxidizing atmospheres, which can be used in industrial plants such as chemical plants as well as various fields of human life.
2. Description of the Prior Art
Some of the present inventors have so far found various amorphous alloys having high corrosion resistance in hot concentrated acids. These alloys are classified into two groups, that is, amorphous metal-metalloid alloys and metal-metal alloys. Amorphous metal-metalloid alloys are composed of iron group elements such as Fe, Co and Ni and 10-25 atomic percent of metalloid elements such as P, C, Si and B. Their high corrosion resistance in aqueous solutions is obtained by the addition of chromium. By contrast, amorphous metal-metal alloys are formed by alloying of Fe, Co, Ni, Cu and/or Al with IVa and Va group elements such as Ta, Nb, Zr and Ti. Their corrosion resistance in aqueous solutions is due to the presence of valve metals.
Some of the present inventors and coinventors in preparing a number of novel amorphous alloys found that alloys in which the melting point of one of the alloy constituents far exceeds the boiling point of another alloy constituent can be prepared by utilizing a sputter-deposition method, since sputtering does not require melting for alloy formation. Some of the present inventors and coinventors thus succeeded to in preparing amorphous Cu- and Al-based alloys with IVa, Va and VIa group elements such as Ti, Zr, Nb, Ta, Mo and W, and applied for Japanese Patent Application Nos. 103296/87, 515567/88, 51568/88 and 260020/88 for these alloys. Some of the present inventors and coinventors further continued to study the preparation of various amorphous alloys and succeeded in preparing amorphous Cr-base alloys with Ti, Zr, Nb, Ta and Al. They applied for Japanese Patent Application Nos. 138575/91, 267542/91, 29362/92 and 29365/92 for these alloys.
Aluminum forms the most stable and protective oxide scale in oxidizing atmospheres at high temperatures, and chromium is the second best element for oxidation resistance among conventional elements. Accordingly, alloys containing these elements have been used in highly oxidizing gas atmospheres at high temperatures. However, aluminum and chromium sulfides are not highly protective, and aluminum sulfide decomposes when it is exposed to a humid atmosphere.
On the other hand, elements which can form stable sulfide scales in highly sulfidizing atmospheres at high temperatures are Mo, W, Nb and Ta. However, when these elements are exposed to oxidizing atmospheres, sublimation of oxides for Mo and W, and breakaway of oxides for Nb and Ta readily occur.
In practical hot corrosion atmospheres, the partial pressures of sulfur vapor and oxygen change drastically. Nevertheless, there were no metallic materials which have sufficiently high resistance against hot corrosion in both sulfidizing and oxidizing atmospheres at high temperatures.
Consequently, there has been a strong demand for further new metallic materials having a high resistance against hot corrosion and which can be used in both sulfidizing and oxidizing atmospheres at high temperatures.